Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$127.88	7.293%	$137.2063	$137.21	$137.20	$137.20
Purchase #2	$65.90	12.772%	$74.3167	$74.32	$74.30	$74.30
Purchase #3	$226.31	7.435%	$243.1361	$243.14	$243.15	$243.10
Purchase #4	$198.39	3.488%	$205.3098	$205.31	$205.30	$205.30
Purchase #5	$53.72	11.835%	$60.0778	$60.08	$60.10	$60.10
Purchase #6	$245.41	10.680%	$271.6198	$271.62	$271.60	$271.60
Purchase #7	$101.87	9.608%	$111.6577	$111.66	$111.65	$111.70
7 purchase totals =	$1,019.48		$1,103.3242	$1,103.34	$1,103.30	$1,103.30